The present invention relates to a picture display device and more particularly the invention relates to a flat plate display device in which the electron beams emitted from a plurality of linear thermionic cathodes are controlled by a plurality of electron beam control electrodes so as to focus, deflect, accelerate and then impinge the electron beams on a fluorescent screen and thereby to display a picture on the screen with a high degree of resolution.
Conventionally, matrix type flat plate display devices of the types employing EL, plasma, liquid crystal, etc., have been developed and these devices have been insufficient in their performance with respect to brightness, light emitting efficiency, color display, etc., thus failing to reach the stage of use in practical applications such as the display of pictures, e.g., TV actions.
On the other hand, attempts to provide flat plate display devices of the type using electron beams have been reported. In other words, a device of this type is designed such that the electron beams emitted from an electron source are controlled by a matrix of flat plate electron beam control electrodes to display characters or a picture.
In U.S. Pat. No. 3,678,330 a display device is disclosed in which electron beams are emitted from a flat plate electron source and a plurality of electron beam control electrode plates each having electrodes arranged in a comblike manner are placed one upon another, whereby the passage of the electron beams is controlled and the beams are accelerated to illuminate a display plate coated with a fluorescent substance and thereby to display characters or a picture on the display plate. A disadvantage of this display device is that it is difficult to obtain a high-current-density flat plate electron source capable of ensuring a uniform current density over the entire display screen.
Generally, with the above type of display device or so-called matrix type display device, the resolution of the picture is dependent on the size and pitch of the apertures provided through the electron beam control electrodes or the base plates of the electrodes. Therefore, it is necessary to reduce the size and pitch of the apertures to produce a picture having a high degree of resolution as well as the sharp detail. When it is intended to produce a sharp picture of a certain size, it is necessary to form the apertures with a greater density and also to greatly increase the number of the apertures as well as the number of the electrodes. For instance, in order to make a display of a picture by television, the mimimum number of the required apertures must be 500.times.750 and the electron beam control electrode plates must be provided with 500 horizontal electrodes and 750 vertical electrodes. Moreover, in order to display a color picture, it is necessary to increase by three times the number of the apertures as well as the number of the electrodes.
With the presently available materials and processing techniques, the maximum limit of the number of electrodes has been considered about 2 to 3 per millimeter, thus failing to ensure a satisfactory resolution. Increasing the number of apertures and the number of electrodes greatly increases the number of drive circuits for driving the electrodes and the number of connections between the drive circuits and the electrodes, thus giving rise to serious mounting or packaging problems.
In an attempt to overcome the foregoing deficiencies, a method is disclosed in U.S. Pat. No. 3,935,500 in which the electron beams are controlled by a pair of matrices of electrodes and the electron beams are vertically and horizontally deflected by deflection electrodes. In U.S. Patent, a thermonic cathode is provided for each of the apertures formed in the matrices of electrodes thus giving rise to a serious practical disadvantage that a very large power is required for heating purposes and there are variations in the amount of emitted electron flow among the cathodes.